The present invention relates to safety razors of the type having a plurality of razor blades contained in a unitary cartridge assembly. More particularly, the present invention relates to a razor blade cartridge unit which has desirable shaving characteristics.
Disposable tandem blade razor blade cartridges are disclosed in various prior art references, for example, U.S. Pat. Nos. 3,934,339 and 3,890,704. These references show razor blade cartridges having twin blades with a spacer therebetween to maintain desired geometrical relationships when affixed between cap and seat members. The same references disclose inwardly directed coupling channels along the bottom portion of the seat member to facilitate placement on and attachment to complementary coupling structures on a razor handle.
Another prior art patent, viz., Pat. No. 3,660,893, demonstrates a tandem blade cartridge configuration in which the desired geometrical configuration is retained by placing the blades in tension when mounted in a combination cap and guard frame. This configuration eliminates the need for a spacer member, but does introduce problems associated with movement of the unsupported blade edges, blade processing and unit assembly. A potential advantage of this configuration rests in the feature that shaving debris can pass without obstruction between the cutting edges and out of the cartridge assembly. It also results in a potential cost saving due to the elimination of the spacer member.
United States Patent Application Ser. No. 604,505 filed Aug. 13, 1975, Inventors: Chen and Beddall now U.S. Pat. No. 4,016,648 discloses a design in which the spacer member is eliminated and debris cleared. This unit incorporates alternately spaced inwardly directed depending structures from the cap and seat members. When these are in registration with respective holes or apertures in the blades, there results clamping of the blade assembly without the normal structural obstruction.
Prior art tandem blade cartridge have achieved satisfactory shaving results and provide adequate closeness and comfort for most of the shaving public. However, with those classes of shavers presenting peculiar problems, for example, women shaving underarms and legs and those having uncommonly sensitive skin, it has been found that a different and more suitable geometrical configuration and cartridge design are desirable. In considering this design, certain parameters are controlled to provide desirable shaving characteristics. The principal of these are: tangent angle--the angle formed by a plane tangent to the blade tip and the guard bar and a plane bisecting the edge apex; exposure--the normal distance the blade edge is above (positive) or below (negative) a plane tangent to both the guard and cap members; and spans--the distance between the first blade edge apex and the guard bar and the second blade edge apex and the first apex, respectively. With proper selection of these parameters and the use of a novel guard bar structure, closeness with safety and comfort can be achieved. It is, therefore, an object of the present invention to produce a unitary disposable twin blade cartridge having improved shaving characteristics. It is another object of the invention to provide a cartridge offering increased comfort to the user while meeting normal closeness requirements. Another object of the invention is to provide a cartridge whereby the user can maintain the desired degree of comfort and closeness by controlled use of the safety razor. Yet another object of the invention is to provide an improved twin blade shaving cartridge.